3D & CAD file formats

Readable: STEP, IGES, BREP, STL, OBJ, PLY, GLB, glTF, 3MF, COLLADA, AMF, FBX, 3DS, OFF. Writable: STL, OBJ, PLY, GLB, glTF, 3MF, OFF, USDZ, Scene JSON. STEP, IGES and BREP are read-only on purpose — once exact surfaces have been triangulated, writing the triangles back into a B-rep format produces a file no CAD kernel wants.

A CAD format such as STEP or IGES stores exact mathematical surfaces — a cylinder is a cylinder, at any zoom level. A mesh format such as STL or OBJ stores triangles that approximate those surfaces. Going from CAD to mesh is a one-way trip, and the tessellation tolerance you pick decides how close the approximation gets.

Because the target format has nowhere to put them. STL stores bare unitless triangles: no units, no colour, no part names. OBJ keeps colours only in a separate MTL file. 3MF and glTF do carry units and materials, so pick one of those when that information matters — the table on each format page says which is which.

3MF if your slicer accepts it: it records real units, is watertight by specification, and carries colours and materials that STL cannot. STL remains the universal fallback that every slicer and printer has read for decades, at the cost of being unitless and colourless.

No. STEP, IGES and BREP are parsed by a full CAD geometry kernel compiled to WebAssembly, and mesh formats load through JavaScript parsers — all inside the browser tab. Nothing is installed and nothing is uploaded, which is what makes it usable for confidential geometry.